A note of caution on the use of the LD ratio in myocardial infarction

Different LD1/LD2 ratios for both normal and pathological samples were obtained with two different reagent kits. These ratio differences are due to the substrate formulation and not to the electrophoresis separation technique. In 45 patients with abnormal serum "cardiac" enzymes, results obtained by the two kit methods showed 17% and 50% "flipped ratio" abnormalities as against 78% and 67% abnormalities when the ratios were compared against appropriate reference ranges. The improper use of the LD ratio test is probably the main cause for its diminished diagnostic usefulness.